Transmit power management in shared-communications channel networks

ABSTRACT

A method of ameliorating the hidden node problem in wireless local area networks employing power control is disclosed. The illustrative embodiments function in a variety of ways that have a common theme: while the Data Frames are transmitted at lesser potency, at least one of the control frames—Request-to-Send, Clear-to-Send, and Acknowledgement—associated with the Data Frame are sent at a greater potency. This causes at least one of the “loud” control frames to be heard and decoded by all of the potentially contending stations. And because the control frames carry duration information for the virtual carrier sense mechanism, their reception suppresses transmissions by potentially-contending stations that cannot sense the “quiet” Data Frames.

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of:

[0002] 1. U.S. Provisional Application No. 60/383,750, filed on May 28,2002, Attorney Docket 680-052us, entitled “Method of Optimizing TransmitPower for EDCF Based Wireless Networks,”

[0003] which is also incorporated by reference.

[0004] The following U.S. patent applications are incorporated byreference:

[0005] 2. U.S. patent application Ser. No. ______, filed on Feb. 28,2003, Attorney Docket 680-055us, entitled “Embedding Class of ServiceInformation in MAC Control Frames,” and

[0006] 3. U.S. patent application Ser. No. 10/353,391, filed on Jan. 29,2003, Attorney Docket 680-032us, entitled “Direct Link Protocol inWireless Area Networks.”

FIELD OF THE INVENTION

[0007] The present invention relates to telecommunications in general,and, more particularly, to a technique for power management in networksthat communicate via a shared-communications channel.

BACKGROUND OF THE INVENTION

[0008]FIG. 1 depicts a schematic diagram of an IEEE 802.11-compliantwireless local area network, which comprises: station 101-1, station101-2, which is an access point, and station 101-3. The communicationsbetween station 101-1, station 101-2, and station 101-3 occur within ashared-communications channel, and, therefore, a medium access controlprotocol is used to allocate usage of the channel among the stations.

[0009] In accordance with the IEEE 802.11 standard, one medium accesscontrol protocol used by the stations is carrier sense multiple access.In accordance with carrier sense multiple access, a station desiring totransmit a frame first listens to the channel and transmits only when itfails to sense another transmission.

[0010] For the purposes of this specification, the “potency” of atransmitted frame is defined as the effective spatial reach of thetransmitted frame. As is well-known to those skilled in the art, thepotency of a frame can be adjusted by the transmitter and is affected bythe energy per bit at which the frame is transmitted. When, as in FIG.1, each station is within the transmission range of every other station,carrier sense multiple access works well. In contrast, when everystation is not within transmission range of every other station, as inFIG. 2, carrier sense multiple access might not work as well. Forexample, when station 201-1 transmits a Frame, station 201-3 will notsense it, and, therefore, might begin a transmission that preventsstation 201-2 from correctly receiving either transmission. This isknown as the “hidden” node problem.

[0011] The IEEE 802.11 standard addresses the hidden node problem with amechanism known as Request-to-Send/Clear-to-Send. The message flowassociated with the Request-to-Send/Clear-to-Send mechanism is depictedin FIG. 3.

[0012] In accordance with the Request-to-Send/Clear-to-Send mechanism,station 201-1 sends a Request-to-Send Frame at time t₀ to all of thestations within its transmission range (i.e., station 201-2). TheRequest-to-Send Frame contains a duration value that extends through theduration of the Clear-to-Send Frame and any Data and AcknowledgementFrames that station 201-1 expects will be transmitted as part of itsrequest. All of the stations within the transmission range of station201-1 receive and decode the Request-to-Send Frame to recover the valuein the duration field. The value in the duration field is then used topopulate a timer, called the Network Allocation Vector, which indicateshow long those stations are to refrain from transmitting, regardless ofwhether they sense a transmission in the channel or not.

[0013] In response to the receipt of the Request-to-Send Frame, station201-2 transmits a Clear-to-Send Frame at time t₂ to all of the stationswithin its transmission range (i.e., station 201-1 and station 201-3).The Clear-to-Send Frame contains a duration value that extends throughthe duration of any Data and Acknowledgement Frames that station 201-1desires to transmit. All of the stations within the transmission rangeof station 201-2 receive and decode the Request-to-Send Frame to recoverthe value in the duration field. The value in the duration field is thenused to populate their Network Allocation Vector.

[0014] In this way, the Request-to-Send/Clear-to-Send mechanismaddresses the hidden node problem by ensuring that station 201-3 willnot transmit while station 201-1 is transmitting its Data Frame tostation 201-2.

SUMMARY OF THE INVENTION

[0015] Some IEEE 802.11 compliant stations transmit their frames at afixed level of potency. In contrast, some IEEE 802.11 compliant stations(e.g., 802.11(h) compliant stations, etc.) can adjust the potency oftheir transmitted frames. The stations that can adjust the potency oftheir transmitted frames are advantageous because they can conserveenergy in contrast to stations that cannot adjust the potency of theirtransmitted frames. The conservation of energy is particularlyadvantageous for battery-powered stations such as notebook computers,personal digital assistants, and digital cameras.

[0016] In general, the stations that can adjust the potency of theirtransmitted frames must balance two competing goals:

[0017] (1) the potency must be sufficient to ensure that the intendedrecipient of the frame can receive the frame, and

[0018] (2) the potency should be as small as possible so as to conserveas much energy as possible.

[0019] An unintended and disadvantageous consequence of having a stationdecrease the potency of its transmitted frames is that it increases thelikelihood that a hidden node might exist. In other words, as a stationreduces the potency of its transmitted frames, it increases thelikelihood that its transmissions will not be sensed by another station,and, therefore, becomes a hidden node.

[0020] To overcome this problem, the illustrative embodiment transmitsData Frames with a different level of potency that one or more of thethe medium access control (“MAC”) control frames Request-to-Send,Clear-to-Send, and Acknowledgement Frames associated with the DataFrame. In particular, while the Data Frames are transmitted with lesserpotency, one or more of the medium access control (“MAC”) control framesRequest-to-Send, Clear-to-Send, and Acknowledgement Frames associatedwith the Data Frame are transmitted with greater potency.

[0021] In accordance with the illustrative embodiment of the presentinvention, the potency of a transmitted frame is affected by:

[0022] i. the energy per bit of the frame, or

[0023] ii. the length of the frame, or

[0024] iii. any combination of i and ii.

[0025] In particular, frames with fewer bits are more potent than frameswith more bits because the probability of receiving a frame with a biterror increases with the number of bits in the frame.

[0026] Furthermore, in accordance with the illustrative embodiment ofthe present invention, the energy per bit of a frame is affected by:

[0027] i. the radiated average power level, or

[0028] ii. the bit rate, or

[0029] iii. the coding rate, or

[0030] iv. any combination of i, ii, and iii.

[0031] It will be clear to those skilled in the art how each of thesefactors affects the energy per bit of a frame and how each of thesefactors affects the rate at which the transmitter consumes energy.

[0032] Even though the illustrative embodiments cause some or all of thecontrol frames to be transmitted with greater potency than they mightotherwise be, many of the embodiments will still consume, on average,less energy than stations that transmit both data and control frames ata fixed level of potency.

[0033] Some embodiments of the present invention are useful when anaccess point relays Data Frames between the source and destinationstations, and some embodiments are useful when the access point does notrelay Data Frames (e.g., when the stations communicate directly inaccordance with the direct link protocol, etc.). U.S. patent applicationSer. No. 10/353,391, entitled “Direct Link Protocol in Wireless AreaNetworks,” teaches a direct link protocol.

[0034] The illustrative embodiment of the present invention comprises:wirelessly receiving a first Data Frame via a shared-communicationschannel, wherein said first Data Frame was transmitted with a firstpotency; and wirelessly transmitting a first Acknowledgement Frame intosaid shared-communications channel at a second potency, wherein saidfirst Acknowledgement Frame is transmitted in response to the receipt ofsaid first Data Frame; wherein said second potency is higher than saidfirst potency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 depicts a schematic diagram of a local area network in theprior art in which there is no “hidden” node problem.

[0036]FIG. 2 depicts a schematic diagram of a local area network in theprior art in which there is a hidden node problem.

[0037]FIG. 3 depicts the message flows associated with theRequest-to-Send/Clear-to-Send mechanism for addressing the hidden nodeproblem in FIG. 2.

[0038]FIG. 4 depicts a schematic diagram of a local area network inaccordance with the illustrative embodiments of the present invention.

[0039]FIG. 5 depicts a block diagram of the salient components in astation in accordance with the illustrative embodiments of the presentinvention.

[0040]FIG. 6 depicts the message flows associated with the firstillustrative embodiment of the present invention.

[0041]FIG. 7 depicts the message flows associated with the secondillustrative embodiment of the present invention.

[0042]FIG. 8 depicts the message flows associated with the thirdillustrative embodiment of the present invention.

[0043]FIG. 9 depicts the message flows associated with the fourthillustrative embodiment of the present invention.

[0044]FIG. 10 depicts the message flows associated with the fifthillustrative embodiment of the present invention.

[0045]FIG. 11 depicts the message flows associated with the sixthillustrative embodiment of the present invention.

[0046]FIG. 12 depicts the message flows associated with the seventhillustrative embodiment of the present invention.

[0047]FIG. 13 depicts the message flows associated with the eighthillustrative embodiment of the present invention.

DETAILED DESCRIPTION

[0048]FIG. 4 depicts a schematic diagram of local area network 400 inaccordance with the illustrative embodiments of the present invention.Local area network 400 comprises a plurality of stations, station 401-1through 401-3, that communicate wirelessly via a shared-communicationschannel. In accordance with the illustrative embodiment, all of thestations in the network operate in compliance with the IEEE 802.11standard.

[0049]FIG. 5 depicts a block diagram of the salient components ofstation 401-i, for i=1 to 4, in accordance with illustrative embodimentsof the present invention. Station 401-i is one station in an IEEE802.11-compliant wireless local area network, and, therefore all of theFrames are transmitted by all of the stations in the network incompliance with the IEEE 802.11 standard. It will be clear to thoseskilled in the art, however, after reading this disclosure, how to makeand use embodiments of the present invention that operate in a non-IEEE802.11 compliant network.

[0050] Throughout the course of each of the illustrative embodiments,stations 401-1 through 401-4 are deemed to be stationery and the radiofrequency environment stable. It will be clear to those skilled in theart, after reading this disclosure, how to make and use embodiments ofthe present invention that operate in a network in which one or more ofthe stations move during the course of an atomic operation or in whichthe radio frequency environment changes during the course of an atomicoperation or both.

[0051] Station 401-i comprises: processor 406, host interface 402,transmitter 403, receiver 404, and memory 405, interconnected as shown.Station 401-i is fabricated on one or more integrated circuits andinterfaces with a host computer (not shown) and an antenna (not shown)in well-known fashion.

[0052] Processor 406 is a general-purpose processor that is capable ofexecuting instructions stored in memory 405, of reading data from andwriting data into memory 405, and of executing the tasks described belowand with respect to FIGS. 6 through 13. In some alternative embodimentsof the present invention, processor 406 is a special-purpose processor.In either case, it will be clear to those skilled in the art, afterreading this disclosure, how to make and use processor 406.

[0053] Host interface 402 is a circuit that is capable of receiving dataand instructions from a host computer (not shown) and of relaying themto processor 406. Furthermore, host interface 402 is capable ofreceiving data and instructions from processor 406 and relaying them tothe host computer. It will be clear to those skilled in the art how tomake and use host interface 402.

[0054] Transmitter 403 is a hybrid analog and digital circuit that iscapable of receiving frames from processor 406 and of transmitting theminto the shared-communications channel at times in accordance with IEEE802.11. It will be clear to those skilled in the art, after reading thisdisclosure, how to make and use transmitter 403.

[0055] Receiver 404 is a hybrid analog and digital circuit that iscapable of receiving frames from the shared-communications channel andrelaying them to processor 406. It will be clear to those skilled in theart, after reading this disclosure, how to make and use receiver 404.

[0056] Memory 405 is a non-volatile random-access memory that storedinstructions and data For processor 406. It will be clear to thoseskilled in the art how to make and use memory 405.

[0057]FIGS. 6 through 13 depict message flows in accordance with variousembodiments of the present invention. In each figure, the formatting ofthe text of the name of a Frame indicates how the Frame is transmitted.The styles of text and their meaning is described in Table 1. TABLE 1Character of Frames Transmitted in Accordance with the IllustrativeEmbodiments of the Present Invention Frame italics denotes a Frame thatis transmitted to the access point at lesser potency. Frame bold denotesa Frame that is transmitted at greater potency. Frame no emphasisdenotes a Frame that is transmitted to the desire peer station at lesserpotency. Frame underline denotes a Frame that is transmitted from onepeer to another peer station without being relayed by an access point(i.e., as part of a direct link stream).

[0058] In all of the embodiments, the Request-to-Send, Clear-to-Send,Data, and Acknowledgement Frames comprise a value equal to the remainderof the atomic operation. This enables all of the stations that hear anyof these frames to set their Network Allocation Vectors so that even ifthey can't physically sense the following frames (i.e., are hidden fromstation 401-1), their virtual carrier sense mechanism will prevent theirtransmitting onto them.

[0059] In accordance with the illustrative embodiments, theRequest-to-Send and Clear-to-Send Frames are sent at the same low bitrate, and the Data and Acknowledgement Frames are generally sent thehighest possible bit rate that results in an acceptable probability ofbeing received correctly. It will be clear to those skilled in the arthow to make and use embodiments of the present invention in which thebit rates of the various frames are sent at different bit rates than inthe illustrative embodiments.

[0060]FIG. 6 depicts the message flows in the first illustrativeembodiment of the present invention. In accordance with the firstillustrative embodiment of the present invention, station 401-2 (theaccess point) is involved in the transmission and reception of all ofthe Request-to-Send, Clear-to-Send, Data, and Acknowledgement Frames.

[0061] At time ₀, station 401-1 transmits a Request-to-Send Frame tostation 401-2 at a first potency. The Request-to-Send Frame is receivedby station 401-2 at time t₁.

[0062] At time t₂, station 401-2 transmits a Clear-to-Send Frame at asecond potency. The second potency is higher than the first potency. TheClear-to-Send Frame is received at time t₃.

[0063] At time t₄, station 401-1 transmits a Data Frame to station 401-2at a third potency. The Data Frame is received by station 401-2 at timet₅. The third potency is equal to the first potency and less than thesecond potency.

[0064] At time t₆, station 401-2 re-transmits the Data Frame to station401-3 at a fourth potency. The Data Frame is received by station 401-3at time t₇.

[0065] At time t₈, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fifth potency, in response to the receipt of the DataFrame. The fifth potency is equal to the fourth potency and less thanthe second potency. The Acknowledgement Frame is received by station401-2 at time t₉.

[0066] At time t₁₀, station 401-2 re-transmits the Acknowledgement Frameto station 401-1 at a sixth potency. The sixth potency is equal to thefirst and third potency and less than the second potency. TheAcknowledgement Frame is received by station 401-1, in response to thereceipt of the Data Frame, at time t₁₁.

[0067] After time t₁₁, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0068]FIG. 7 depicts the message flows in the second illustrativeembodiment of the present invention. In accordance with the secondillustrative embodiment of the present invention, station 401-2 (theaccess point) is involved in the transmission and reception of all ofthe Request-to-Send, Clear-to-Send, Data, and Acknowledgement Frames.

[0069] At time t₀, station 401-1 transmits a Request-to-Send Frame tostation 401-2 at a first potency. The Request-to-Send Frame is receivedby station 401-2 at time t₁.

[0070] At time t₂, station 401-2 transmits a Clear-to-Send Frame at asecond potency. The second potency is higher than the first potency. TheClear-to-Send Frame is received at time t₃.

[0071] At time t₄, station 401-1 transmits a Data Frame to station 401-2at a third potency. The Data Frame is received by station 401-2 at timet₅. The third potency is equal to the first potency and less than thesecond potency.

[0072] At time t₆, station 401-2 re-transmits the Data Frame to station401-3 at a fourth potency. The Data Frame is received by station 401-3at time t₇.

[0073] At time t₈, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fifth potency, in response to the receipt of the DataFrame The fifth potency is higher than the fourth potency and equal tothe second potency. The Acknowledgement Frame is received by station401-2 at time t₉.

[0074] At time t₁₀, station 401-2 re-transmits the Acknowledgement Frameto station 401-1 at a sixth potency. The sixth potency is higher thanthe first and third potency and equal to the second potency. TheAcknowledgement Frame is received by station 401-1, in response to thereceipt of the Data Frame, at time t₁₁.

[0075] After time t₁₁, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0076]FIG. 8 depicts the message flows in the third illustrativeembodiment of the present invention. In accordance with the thirdillustrative embodiment of the present invention, station 401-2 (theaccess point) is involved in the transmission and reception of all ofthe Data and Acknowledgement Frames. In accordance with the thirdillustrative embodiment, there are no transmitted Request-to-Send Framesor Clear-to-Send Frames. This is particularly useful when the first DataFrame of a contention free burst is a short frame because both the DataFrames and the Acknowledgement Frames convey the duration informationfor the remainder of the burst.

[0077] At time ₀, station 401-1 transmits a Data Frame to station 401-2at a first potency. The Data Frame is received by station 401-2 at timet₁.

[0078] At time t₂, station 401-2 re-transmits the Data Frame to station401-3 at a second potency. The Data Frame is received by station 401-3at time t₃.

[0079] At time t₄, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a third potency, in response to the receipt of the DataFrame The third potency is higher than the second potency. TheAcknowledgement Frame is received by station 401-2 at time t₅.

[0080] At time t₆, station 401-2 re-transmits the Acknowledgement Frameto station 401-1 at a fourth potency. The fourth potency is higher thanthe first potency. The Acknowledgement Frame is received by station401-1, in response to the transmission of the Data Frame, at time t₇.

[0081] After time t₈, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0082]FIG. 9 depicts the message flows in the fourth illustrativeembodiment of the present invention. In accordance with the fourthillustrative embodiment, station 401-1 and station 401-3 communicatedirectly and without station 401-2.

[0083] At time ₀, station 401-1 transmits a Request-to-Send Frame tostation 401-3 at a first potency. The Request-to-Send Frame is receivedby station 401-3 at time t₁.

[0084] At time t₂, station 401-3 transmits a Clear-to-Send Frame at asecond potency. The Clear-to-Send Frame is received by station 401-1 attime t₃.

[0085] At time t₄, station 401-1 transmits a Data Frame to station 401-3at a third potency. The Data Frame is received by station 401-3 at timet₅. The third potency is lower than to the first potency.

[0086] At time t₆, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fourth potency, in response to the receipt of theData Frame. The Acknowledgement Frame is received by station 401-3 attime t₇. The fourth potency is less than the first potency and thesecond potency and equal to the third potency.

[0087] After time t₁₁, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0088]FIG. 10 depicts the message flows in the fifth illustrativeembodiment of the present invention. In accordance with the fifthillustrative embodiment, station 401-1 and station 401-3 communicatedirectly and without station 401-2.

[0089] At time t₀, station 401-1 transmits a Request-to-Send Frame tostation 401-3 at a first potency. The Request-to-Send Frame is receivedby station 401-3 at time t₁.

[0090] At time t₂, station 401-3 transmits a Clear-to-Send Frame at asecond potency. The second potency is lower than the first potency. TheClear-to-Send Frame is received by station 401-1 at time t₃.

[0091] At time t₄, station 401-1 transmits a Data Frame to station 401-3at a third potency. The Data Frame is received by station 401-3 at timet₅. The third potency is lower than to the first potency and equal tothe second potency.

[0092] At time t₆, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fourth potency, in response to the receipt of theData Frame. The Acknowledgement Frame is received by station 401-3 attime t₇. The fourth potency is less than the first potency and equal tothe second and third potency.

[0093] After time t₁₁, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0094]FIG. 11 depicts the message flows in a sixth illustrativeembodiment of the present invention. In accordance with the sixthillustrative embodiment, station 401-1 and station 401-3 communicatedirectly and without station 401-2.

[0095] At time t₀, station 401-1 transmits a Request-to-Send Frame tostation 401-3 at a first potency. The Request-to-Send Frame is receivedby station 401-3 at time t₁.

[0096] At time t₂, station 401-3 transmits a Clear-to-Send Frame at asecond potency. The second potency is higher than the first signal tonoise ratio. The Clear-to-Send Frame is received by station 401-1 attime t₃.

[0097] At time t₄, station 401-1 transmits a Data Frame to station 401-3at a third potency. The Data Frame is received by station 401-3 at timet₅. The third potency is equal to the first potency and lower than thesecond potency.

[0098] At time t₆, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fourth potency, in response to the receipt of theData Frame. The Acknowledgement Frame is received by station 401-3 attime t₇. The fourth potency is less than the second potency and equal tothe first and third potencies.

[0099] After time t₁₁, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0100]FIG. 12 depicts the message flows in a seventh illustrativeembodiment of the present invention. In accordance with the fourthillustrative embodiment, station 401-2 is involved in theRequest-to-Send and Clear-to-Send Frame flow, but stations 401-1 and401-3 transmit the Data and Acknowledgement Frames directly and withoutstation 401-2.

[0101] At time ₀, station 401-1 transmits a Request-to-Send Frame tostation 401-2 at a first potency. The Request-to-Send Frame is receivedby station 401-2 at time t₁.

[0102] At time t₂, station 401-2 transmits a Clear-to-Send Frame at asecond signal-to-noise. The second potency is equal to the firstpotency. The Clear-to-Send Frame is received by station 401-1 andstation 401-2 at time t₃.

[0103] At time t₄, station 401-1 transmits a Data Frame to station 401-3at a third potency, which is received by station 401-3 at time t₅. Thethird potency is lower than the first potency.

[0104] At time t₆, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fourth potency, in response to the receipt of theData Frame. The fourth potency is equal to the third potency. TheAcknowledgement Frame is received by station 401-3 at time t₇ inresponse to the transmission of the Data Frame.

[0105] After time t₇, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0106]FIG. 13 depicts the message flows in the eighth illustrativeembodiment of the present invention. In accordance with the firstillustrative embodiment of the present invention, station 401-2 (theaccess point) is all involved in the transmission and reception of theRequest-to-Send, Clear-to-Send, data, and Acknowledgement Frames. First,station 401-1 transmits a Data Frame to station 401-3 via station 401-2,and then station 401-3 transmits a Data Frame to station 401-1. Thepoint of this illustrative embodiment is to show the symmetry associatedwith the transmission of Data Frames.

[0107] At time t₀, station 401-1 transmits a Request-to-Send Frame tostation 401-2 at a first potency. The Request-to-Send Frame is receivedby station 401-2 at time t₁.

[0108] At time t₂, station 401-2 transmits a Clear-to-Send Frame at asecond potency. The Clear-to-Send Frame is received at time t₃.

[0109] At time t₄, station 401-1 transmits a Data Frame to station 401-2at a third potency, which is received by station 401-2 at time t₅. Thethird potency is less than the first potency.

[0110] At time t₆, station 401-2 re-transmits the Data Frame to station401-3 at a fourth potency The fourth potency is less than the secondpotency. The Data Frame is received by station 401-3 at time t₇.

[0111] At time t₈, station 401-3 transmits an Acknowledgement Frame tostation 401-2 at a fifth potency, in response to the receipt of the DataFrame. The Acknowledgement Frame is received by station 401-2 at timet₉. The fifth potency is higher than the fourth potency.

[0112] At time t₁₀, station 401-2 re-transmits the Acknowledgement Frameto station 401-1 at a sixth potency. The Acknowledgement Frame isreceived by station 401-1 at time t₁₁. The sixth potency is higher thanthe third potency.

[0113] After time t₁₁, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0114] At time t₁₂, station 401-3 transmits a Request-to-Send Frame tostation 401-2 at a seventh potency. The Request-to-Send Frame isreceived by station 401-2 at time t₁₃. The seventh potency equals thefifth potency.

[0115] At time t₁₄, station 401-2 transmits a Clear-to-Send Frame at aeighth potency. The eighth potency is equal to the second potency. TheClear-to-Send Frame is received at time t₁₅.

[0116] At time t₁₆, station 401-3 transmits a Data Frame to station401-2 at a ninth potency. The Data Frame is received by station 401-2 attime t₁₇. The ninth potency is equal to the fourth potency and less thanthe fifth and seventh potencies.

[0117] At time t₁₈, station 401-2 re-transmits the Data Frame to station401-1 at a tenth potency. The Data Frame is received by station 401-1 attime t₁₉. The tenth potency is equal to the third potency and less thanthe first and sixth potencies.

[0118] At time t₂₀, station 401-1 transmits an Acknowledgement Frame tostation 401-2 at an eleventh potency, in response to the receipt of theData Frame. The Acknowledgement Frame is received by station 401-2 attime t₂₁. The eleventh potency is higher than the third and tenthpotencies and equal to the first and sixth potencies.

[0119] At time t₂₁, station 401-2 re-transmits the Acknowledgement Frameto station 401-3 at a twelfth potency. The Acknowledgement Frame isreceived by station 401-1 at time t₂₂. The twelfth potency is higherthan the fourth and ninth potencies and equal to the fifth and seventhpotencies.

[0120] After time t₂₂, the network allocation vector in all of thestations that received any frame in the process will have expired, and,therefore contention for the shared-communications channel can resume inwell-known fashion unless more Data Frames are to be transmitted as partof a contention free burst. In the case of a contention free burst, thesecond and subsequent Data Frames are protected when stations 401-1,401-2, and 401-3 transmit a frame containing the duration of theremainder of the burst. It will be clear to those skilled in the art howto make and use embodiments of the present invention that accommodatecontention free bursts.

[0121] It is to be understood that the above-described embodiments aremerely illustrative of the present invention and that many variations ofthe above-described embodiments can be devised by those skilled in theart without departing from the scope of the present invention. It istherefore intended that such variations be included within the scope ofthe following claims and their equivalents.

What is claimed is:
 1. A method comprising: wirelessly receiving a firstData Frame via a shared-communications channel, wherein said first DataFrame was transmitted with a first potency; and wirelessly transmittinga first Acknowledgement Frame into said shared-communications channel ata second potency, wherein said first Acknowledgement Frame istransmitted in response to the receipt of said first Data Frame; whereinsaid second potency is higher than said first potency.
 2. The method ofclaim 1 wherein said Data Frame and said Acknowledgement Frame are bothtransmitted in compliance with an IEEE 802.11 standard.
 3. The method ofclaim 1 wherein the bit rate of said first Data Frame is higher than thebit rate of said first Acknowledgement Frame.
 4. The method of claim 1further comprising: wirelessly transmitting a second Data Frame intosaid shared-communications channel at a third potency; and wirelesslyreceiving a second Acknowledgement Frame via said shared-communicationschannel at a fourth potency, wherein said second Acknowledgement Framewas transmitted in response to the receipt of said second Data Frame;wherein said fourth potency is higher than said third potency.
 5. Themethod of claim 1 wherein the bit rate of said second Data Frame ishigher than the bit rate of said second Acknowledgement Frame.
 6. Amethod comprising: wirelessly transmitting a first Data Frame into ashared-communications channel, wherein said first Data Frame wastransmitted with a first potency; and wirelessly receiving a firstAcknowledgement Frame via said shared-communications channel at a secondpotency, wherein said first Acknowledgement Frame is transmitted inresponse to the transmission of said first Data Frame; wherein saidsecond potency is higher than said first potency.
 7. The method of claim1 wherein said Data Frame and said Acknowledgement Frame are bothtransmitted in compliance with an IEEE 802.11 standard.
 8. The method ofclaim 1 wherein the bit rate of said first Data Frame is higher than thebit rate of said first Acknowledgement Frame.
 9. The method of claim 1further comprising: wirelessly receiving a second Data Frame via saidshared-communications channel at a third potency; and wirelesslytransmitting a second Acknowledgement Frame into saidshared-communications channel at a fourth potency, wherein said secondAcknowledgement Frame was transmitted in response to the receipt of saidData Frame; wherein said fourth potency is higher than said thirdpotency.
 10. The method of claim 1 wherein the bit rate of said secondData Frame is higher than the bit rate of said second AcknowledgementFrame.
 11. An apparatus comprising: a wireless receiver for receiving afirst Data Frame and a first Acknowledgement Frame from a first stationvia a shared-communications channel, wherein said first Data Frame istransmitted at a first potency and said first Acknowledgement Frame istransmitted at a second potency; and a wireless transmitter fortransmitting a second Data Frame and a second Acknowledgement to saidfirst station via said shared-communications channel, wherein saidsecond Data Frame is transmitted at a third signal-to-noise-ratio andsaid second Acknowledgement Frame is transmitted at a fourth potency;wherein said second Acknowledgement is transmitted in response to thereceipt of said first Data Frame; wherein said first Acknowledgement isreceived in response to the transmission of said second Data Frame;wherein said fourth potency is higher than said first potency; andwherein said second potency is higher than said third potency.
 12. Theapparatus of claim 6 wherein said first Data Frame, said second DataFrame, said first Acknowledgement Frame, and said third AcknowledgementFrame are all transmitted in compliance with an IEEE 802.11 standard.13. The apparatus of claim 6 wherein the bit rate of said first DataFrame is higher than the bit rate of said second Acknowledgement Frame;and wherein the bit rate of said second Data Frame is higher than thebit rate of said first Acknowledgement Frame.
 14. A method comprising:wirelessly transmitting a Request-to-Send Frame from a first station toan access point via a shared-communications channel, wherein saidRequest-to-Send Frame is transmitted at a first potency, wherein saidfirst potency is sufficient to enable said access point to decode saidRequest-to-Send Frame, and wherein said first potency is insufficient toenable a second station to decode said Request-to-Send Frame; wirelesslyreceiving at said first station a Clear-to-Send Frame from said accesspoint via said shared-communications channel, wherein said Clear-to-SendFrame is transmitted at a second potency that is sufficient to enableboth said first station and said second station to decode saidClear-to-Send Frame; wirelessly transmitting a Data Frame from a firststation to said access point via said shared-communications channel,wherein said Data Frame is transmitted at a third potency, wherein saidthird potency is sufficient to enable said access point to decode saidData Frame, and wherein said third potency is insufficient to enablesaid second station to decode said Data Frame; and wirelessly receivingat said first station an Acknowledgement Frame from said access pointvia shared-communications channel, wherein said Acknowledgement Frame istransmitted at a fourth potency that is sufficient to enable said firststation to decode said Acknowledgement Frame, and wherein said fourthpotency is insufficient to enable said second station to decode saidAcknowledgement Frame.
 15. The method of claim 14 wherein saidRequest-to-Send Frame, said Clear-to-Send Frame, said Data Frame, andsaid Acknowledgement Frame are all are all transmitted in compliancewith an IEEE 802.11 standard.
 16. The method of claim 14 wherein saidsecond potency is greater than said fourth potency.
 17. A methodcomprising: wirelessly transmitting a Request-to-Send Frame from a firststation to an second station via a shared-communications channel,wherein said Request-to-Send Frame is transmitted at a first potency,wherein said first potency is sufficient to enable said second stationto decode said Request-to-Send Frame, and wherein said first potency isinsufficient to enable an access point to decode said Request-to-SendFrame; wirelessly receiving at said first station a Clear-to-Send Framefrom said second station via said shared-communications channel, whereinsaid Clear-to-Send Frame is transmitted at a second potency that issufficient to enable both said first station and said access point todecode said Clear-to-Send Frame; wirelessly transmitting a Data Framefrom a first station to said second station via saidshared-communications channel, wherein said Data Frame is transmitted ata third potency, wherein said third potency is sufficient to enable saidsecond station to decode said Data Frame, and wherein said third potencyis insufficient to enable said access point to decode said Data Frame;and wirelessly receiving at said first station an Acknowledgement Framefrom said second station via shared-communications channel, wherein saidAcknowledgement Frame is transmitted at a fourth potency that issufficient to enable said first station to decode said AcknowledgementFrame, and wherein said fourth potency is insufficient to enable saidaccess point to decode said Acknowledgement Frame.
 18. The method ofclaim 17 wherein said Request-to-Send Frame, said Clear-to-Send Frame,said Data Frame, and said Acknowledgement Frame are all transmitted incompliance with an IEEE 802.11 standard.
 19. The method of claim 17wherein said second potency is greater than said fourth potency.